Healing transmyocardial implant

ABSTRACT

A transmyocardial implant establishes a blood flow path through a myocardium between a heart chamber and a lumen of a coronary vessel residing on an exterior of the heart. The implant includes a coronary portion sized to be received within the vessel. A myocardial portion is sized to pass through the myocardium into the heart chamber. A transition portion connects the coronary and myocardial portions for directing blood flow from the myocardial portion to the coronary portion. The coronary portion and the myocardial portion have an open construction for permitting tissue growth across a wall thickness of the coronary portion and the myocardial portion. The myocardial portion includes an agent for controlling a coagulation cascade and platelet formation.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention pertains to an implant for passing blood flowdirectly between a chamber of the heart and a coronary vessel. Moreparticularly, this invention pertains to such an implant with an enhancedesign for promoting a healed layer of cells on an interior of theimplant.

[0003] 2. Description of the Prior Art

[0004] Commonly assigned U.S. Pat. No. 5,755,682 issued May 26, 1998 andcommonly assigned and co-pending U.S. patent application Ser. No.08/882,397 filed Jun. 25, 1997, entitled “Method and Apparatus forPerforming Coronary Bypass Surgery”, and filed in the name of inventorsMark B. Knudson and William L. Giese (published as PCT InternationalApplication Publication No. WO 98/06356) both teach an implant fordefining a blood flow conduit directly from a chamber of the heart to alumen of a coronary vessel. In one embodiment, an L-shaped implant isreceived within a lumen of a coronary artery and passed through themyocardium to extend into the left ventricle of the heart. The conduitis rigid and remains open for blood flow to pass through the conduitduring both systole and diastole. The conduit penetrates into the leftventricle in order to prevent tissue growth and occlusions over anopening of the conduit. The '682 patent and '397 application alsodescribe an embodiment where a portion of the implant passing throughthe heart wall is an open structural member lined by polyester (e.g.,Dacron). A further embodiment discloses a portion of the implant in acoronary vessel as being an open cell, balloon-expandable stent.

[0005] U.S. Pat. No. 5,429,144 to Wilk dated Jul. 4, 1995 teachesimplants which are passed through the vasculature in a collapsed stateand expanded when placed in the myocardium so as not to extend intoeither the coronary artery or the left ventricle. The described implantsclose once per cycle of the heart (e.g., during diastole in theembodiment of FIGS. 7A and 7B or during systole in the embodiment ofFIGS. 2A and 2B). Either of these two designs may be lined with a graft.

[0006] Commonly assigned and co-pending U.S. patent application Ser. No.08/944,313 filed Oct. 6, 1997, entitled “Transmyocardial Implant”, andfiled in the name of inventors Katherine S. Tweden, Guy P. Vanney andThomas L. Odland, teaches an implant such as that shown in theaforementioned '397 application and '682 patent with an enhancedfixation structure. The enhanced fixation structure includes a fabricsurrounding at least a portion of the conduit to facilitate tissuegrowth on the exterior of the implant.

[0007] PCT International Application Publication No. WO 98/08456describes a protrusive stent to form a passageway from the heart to acoronary vessel. The stent is described as wire mesh or other metal orpolymeric material and may be self-expanding or pressure expandable. Theapplication describes the stent may be covered by a partial or completetubular covering of material including polyester, woven polyester,polytetraflouroethylene, expanded polytetraflouroethylene, polyurethane,silicone, polycarbonate, autologous tissue and xenograft tissue.

[0008] Biocompatibility is an important design feature. Solid metalimplants are formed of material (e.g., titanium or pyrolytic carbon)with low incidents of thrombus and platelet activation. While suchmaterials are proven in use in a wide variety of products (e.g., heartvalve components), they do not facilitate full healing. By “healing”, itis meant that over time, the patient's cells grow over the material ofthe implant so that blood flowing through the implant is exposed only(or at least primarily) to the patient's cells rather than to a foreignmaterial.

SUMMARY OF THE INVENTION

[0009] According to a preferred embodiment of the present invention, atransmyocardial implant is disclosed for establishing a blood flow paththrough a myocardium between a heart chamber and a lumen of a coronaryvessel residing on an exterior of the heart. The implant includes acoronary portion sized to be received with the vessel. A myocardialportion is sized to pass through the myocardium into the heart chamber.A transition portion connects the coronary and myocardial portions fordirecting blood flow from the myocardial portion and into the coronaryportion. The coronary portion and the myocardial portion have an openconstruction for permitting tissue growth across a wall thickness of thecoronary portion and the myocardial portion. The myocardial portionincludes an agent for controlling the coagulation cascade and plateletactivation, and promoting healing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a side-elevation view of a transmyocardial implantaccording to the present invention shown in place defining a blood flowpath from a left ventricle to a coronary artery;

[0011]FIG. 2 is a cross-sectional view of the implant of FIG. 1;

[0012]FIG. 3 is a view of an alternative embodiment of the implant ofFIG. 1 illustrating a portion of the implant expandable within acoronary artery;

[0013]FIG. 4 is a view similar to FIG. 3 showing a transition portion ofopen cell construction;

[0014]FIG. 5 is a side section view of an alternative embodiment of FIG.3 showing a balloon catheter admitted into the implant through an accessport; and

[0015]FIG. 6 is a side sectional view of an expandable implant with aballoon catheter removable through a myocardial portion of the catheter.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0016] With initial reference to FIG. 1, a conduit 10 is shown in theform of an L-shaped tube. The conduit 10 may be formed of titanium orother biocompatible material. The material of the conduit 10 ispreferably radially rigid material in order to withstand contractionforces of the myocardium. By way of non-limiting example, the tube willhave an outside diameter D_(O) of about 3 millimeters and an internaldiameter D_(I) of about 2.5 millimeters to provide a wall thickness ofabout 0.25 millimeters.

[0017] The tube 10 has a coronary portion 12 sized to be received withinthe lumen of a coronary vessel such as the lumen 80 of a coronary artery82 distal to an obstruction 81 as illustrated in FIG. 1. The conduit 10has a myocardial portion 14 extending at a right angle to the axis ofportion 12. The myocardial portion 14 is sized to extend from thecoronary artery 82 directly through the myocardium 84 and protrude intothe left ventricle 83 of a patient's heart.

[0018] The coronary portion 12 has a first opening 16. The myocardialportion 14 has a second opening 18 in communication with an interior 20of the implant 10. Therefore, blood can freely flow through the implant10 between the left ventricle 83 and the lumen 80 of the coronary artery82. Blood flows axially out of opening 16 parallel with the axis oflumen 80.

[0019] The longitudinal axis of the coronary portion 12 is aligned withthe axis of the lumen 80. Sutures 24 secure the artery 82 to thecoronary portion 12. The proximal portion 82 a of the coronary artery isligated by sutures 85.

[0020] The coronary and myocardial portions 12, 14 have an open latticeconstruction 12 a, 14 a to define a plurality of open cells 12 b, 14 bextending through the wall thickness of the implant 10. Preferably, thecoronary and myocardial portions 12, 14 are joined by a transitionportion 13 in a 90° bend between portions 12, 14. While transitionportion 13 can have an open lattice construction as portions 12, 14,transition portion 13 will preferably have smaller open areas in such anopen construction or, as illustrated, will be of solid construction.Such construction permits the transition portion to deflect highvelocity blood flows from the myocardial portion 14 into the coronaryportion 12. A lattice construction with large open cells in thetransition portion could result in the high velocity flow damagingtissue (not shown) overlying the transition portion.

[0021] Any one or all of the coronary portion 12, transition portion 13and myocardial portion 14 could be formed in final size as rigid unitsor could be formed in small diameter sizes which are subsequentlyexpanded to full size. For example, FIG. 3 illustrates a coronaryportion 12′ which is formed tapering from the transition portion 13′ toa reduced diameter open end 16′. The taper permits ease of insertioninto a coronary artery. Following such insertion, the tapered coronaryportion 12′ may be expanded to full size illustrated by the phantomlines in FIG. 3. Such expansion can be performed using balloon-tippedcatheters as is conventional in stent angioplasty. A collapsed andsubsequently expanded implant 10 where all portions 12, 13 and 14 areexpanded can permit use as a percutaneously deployed implant. Thepresent drawings illustrate a presently preferred surgically deployedimplant. In the surgical application, the artery 82 is ligated. Theimplant 10 is passed through the epicardium and myocardium on a side ofthe artery 82.

[0022]FIG. 5 illustrates a balloon 100 placed in a tapered coronaryportion 12. A lead 102 from the balloon 100 is passed through an opening113′ in the transition portion 13′. The opening 113′ can be closed witha plug 115′ after the balloon 100 and lead 102 are withdrawn through theopening 113′.

[0023] Alternatively, in a transition portion 13″ with open cellconstruction (FIG. 4), the balloon lead can be passed through theopenings of the transition portion 113″. FIG. 6 illustrates passing thelead 102 through opening 18 of the myocardial portion. The lead 102 canbe pulled upwardly from the exterior of the heart to remove the balloon100. Alternatively, the lead 102 can be pulled through a catheter (notshown) adjacent end 18 in the left ventricle.

[0024] In either percutaneous or surgical implants, a flexibletransition portion 13 (as would be achieved with a stent latticeconstruction) permits relative articulation between the coronary andmyocardial portions 12, 14 to ensure the coronary portion is axiallyaligned with the lumen 80. Absent such articulation, such axialalignment is achieved by accurately controlling the position of themyocardial portion 14 such that the coronary portion 12 is axiallyaligned with the lumen 80 following implantation.

[0025] The open cell construction of the coronary and myocardialportions 12, 14 permit tissue growth through the open cells 12 c, 14 cfollowing implant. The healing procedure in the coronary portion 12 isthe same as that in coronary stents. Vascular endothelial cells growover to coat the structural material 12 a of portion 12.

[0026] In portion 14, myocardial tissue, if not obstructed, will growthrough the cells 14 c. Furthermore, the myocardium is highlythrombogenic. Therefore, uncontrolled contact between the myocardium 82and the implant interior 20 can result in thrombosis of the implant 10.Further, it is believed that the epicardium (i.e., outer layer of themyocardium) has a greater density of myocardial growth cells whichcontribute to healing.

[0027] To control growth in the myocardial portion 14, a liner 30 isprovided in the myocardial portion 14. The liner 30 is any porousmaterial for accepting tissue growth and, preferably, is a polyesterfabric (e.g., Dacron). The porous liner 30 has interstial spaces smallerthan the open cells 12 c, 14 c. The liner 30 is shown on an interior ofthe myocardial portion 14 but could also or alternatively surround theexterior.

[0028] The liner 30 has an upper end 32 secured through any suitablemeans (e.g., sutures not shown) to the upper end of the myocardialportion 14. A lower end 34 is folded over the opening of the myocardialportion 14 and secured to the exterior of the portion 14 by sutures 36.The myocardial portion 14 is sized to protrude into the left ventricle83 with only the folded over liner material exposed to the interior ofthe left ventricle 83.

[0029] The liner 30 acts as a porous substrate into which tissue maygrow. To prevent thrombus, the liner 30 is impregnated with an agent forcontrolling coagulation cascade and platelet activation and adhesion. Anexample of such an agent is heparin but could be any anticoagulant orantiplatelet. Also, an agent such as a basic fibroblast growth factorcould be used to accelerate healing.

[0030] The agent permits structural cells to grow on the liner bylimiting thrombus formation which, uncontrolled, would occlude theimplant. Due to the open construction, the structural, healing cells ofthe epicardium can grow onto the liner. Subsequently, endothelial cellscan grow on the structural cells.

[0031] Therefore, the structure described promotes a three-stage healingprocess:

[0032] 1. the drug agents control healing by minimizing coagulation andplatelet activation which would otherwise be stimulated by agents fromthe myocardium; and

[0033] 2. structural cells grow into and on the liner 30 now lined withthe thrombus to initially heal and form a vascular bed; and

[0034] 3. endothelial cells grow over the structural cells.

[0035] In the transition portion 13, an open cells structure will permittissue growth as in the coronary portion 12. Such growth may also occurin the solid construction. Alternatively, the liner 30 can be extendedinto the transition portion 13. Additionally, the open cell structure inthe transition portion 13 can permit articulation between the coronaryportion and the myocardial portion. Such a structure is shown in FIG. 4.The open transition portion 13″ is formed by a coil 13 a″ between thecoronary portion 12″ and the myocardial portion 14″. This structurepermits bending at the transition portion. As a result, the coronaryportion can be axially aligned in the artery without first accuratelypositioning the myocardial portion.

[0036] Having disclosed the present invention in a preferred embodiment,it will be appreciated that modifications and equivalents may occur toone of ordinary skill in the art having the benefits of the teachings ofthe present invention. It is intended that such modifications shall beincluded within the scope of the claims appended hereto. For example,the liner 30 can take many constructions including PTFE, expanded-PTFE,polyurethane, polypropylene or any biologically compatible pavingmaterial or natural tissue. Further, restenosis of the coronary portion12 can be prevented with radioactivity therapy (such as providing thecoronary portion with a short half-life beta emitter). Also, the liner30 may be either a resorbable or non-resorbable material. Geneticallyengineered cells can be transformed to secrete anticoagulants and otheragents to keep the blood fluid (such as tissue plasminogen activator andsmooth muscle cells altered to express nitric acid).

What is claimed:
 1. A transmyocardial implant for defining a blood flowpathway directly from a left ventricle to a coronary vessel, the implantcomprising: a coronary portion sized to be received within the vessel; amyocardial portion sized to pass through the myocardium into the leftventricle; a transition portion connecting the coronary and myocardialportion for directing blood flow from the myocardial portion to thecoronary portion; at least the coronary portion and the myocardialportion having an open construction for permitting tissue growth acrossa wall thickness of the coronary portion and the myocardial portion; andat least the myocardial portion including an agent for controlling acoagulation cascade and platelet activation.
 2. An implant according toclaim 1 further comprising an agent for encouraging healing.
 3. Animplant according to claim 1 further comprising a porous lining in atleast the myocardial portion with the porous lining have pores smallerthan openings of the open construction of the myocardial portion.
 4. Animplant according to claim 1 wherein the porous lining contains theagent.
 5. An implant according to claim 1 wherein the agent is heparin.6. An implant according to claim 1 wherein the agent is ananti-coagulant.
 7. An implant according to claim 1 wherein the agent isan anti-platelet.
 8. An implant according to claim 2 wherein the agentfor encouraging healing is a growth factor.
 9. An implant according toclaim 1 wherein the coronary portion is expandable from a first diameterto an enlarged second diameter.
 10. An implant according to claim 1wherein the myocardial portion is expandable from a first diameter to anenlarged second diameter.
 11. An implant according to claim 1 whereinthe transition portion permits articulation between the coronary portionand the myocardial portion.
 12. A transmyocardial implant for defining ablood flow pathway directly from a left ventricle to a coronary vessel,the implant comprising: a coronary portion sized to be received withinthe vessel; a myocardial portion sized to pass through the myocardiuminto the left ventricle; a transition portion connecting the coronaryand myocardial portion for directing blood flow from the myocardialportion to the coronary portion; and the myocardial portion including aconstruction to facilitate tissue integration and including an agent forcontrolling a coagulation cascade and platelet activation.
 13. Animplant according to claim 12 wherein the coronary portion includes anopen structure to facilitate growth of vascular endothelial cells alongthe coronary portion.
 14. An implant according to claim 12 wherein themyocardial portion includes a porous structure for facilitating growthof vascular endothelial cells into the myocardial portion.
 15. Animplant according to claim 14 wherein the porous structure includes afabric liner.
 16. An implant according to claim 14 wherein themyocardial portion further includes a wall structure for facilitatinggrowth of structural cells into the interior of the myocardial portion.17. An implant according to claim 16 wherein the wall structure is anopen cell construction of the myocardial portion.